When Earth Moves The sudden movement of Earth’s plates releases energy and triggers an earthquake. Seismic waves ripple through the ground, starting at the hypocenter. The epicenter is the point directly above it at the surface and where most of the damage occurs.
fault epicenter plate hypocenter plate
Earth’s plates
Measuring Quakes A seismograph also measures how strong an earthquake is. T is is called magnitude. Magnitude is measured on a scale of one to ten. On this scale, each number is ten times stronger than the one before it. So a magnitude 7 earthquake moves the ground ten times more than a magnitude 6 quake. T e largest quake ever recorded was magnitude 9.5. T e quake in Haiti was magnitude 7. T e quake in Haiti really shook things up.
It struck Haiti’s densely populated capital and shiſt ed the ground as much as 4 m. T is city was built on soſt soil. Seismic waves rolled through it like waves on an ocean. T e force of the quake turned the soils near the harbor to jelly. Buildings tilted or toppled. Scientists weren’t able to predict this quake,
so they weren’t able to warn anyone it was coming. Quake predictions could save lives.
Predicting Quakes Predicting earthquakes is hard, though. Scientists know most of the faults where quakes are likely to strike. Yet they don’t know when these faults will slip. So they can’t predict when a quake will happen. Lots of people, however, have come up with
odd ways to tell when a quake might happen. Some think that quakes are more likely during a full moon. Others say animals act strangely before a quake. At least one study suggests that some toads
can sense electrical signals or gases escaping from the ground before a quake happens. Yet there’s no scientific proof that these ideas can accurately predict a quake. Many scientists say they’ll never be able to
accurately predict earthquakes. Instead, they say, places near active faults should just be ready all the time.
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